The control of the air-fuel ratio (AFR) is critical for the efficiency of the combustion. This is for achieving the better performance of the plant and result in high output energy. Computation of the AFR is gone considering the composition of the fuel regardless of the inlet pressure, density ad temperature of both fuel and the air. This paper models AFR as a function of the inlet temperature, density, and pressure. Formulated models have been checked using recorded data from the Jabana2 Oil Power Plant. The results show that the AFR increases by 1.5 units as the pressures of the gas increase by 0.6 bars but when it reaches 2.9 bar, AFR starts to decrease, 0.9% of the increase of the density leads to the decrease of the AFR of 0.4 in average. 3.5 degrees Celcius rise of inlet temperature lift the AFR by 0.2; however, it starts to decrease when the temperature reaches 78 degrees Celcius.